Applicants claim priority based upon Czechoslovakian patent application number PV 5464-89 filed on Sep. 26, 1989.
This invention relates generally to a contact lens made of a hydophilic gel and more particularly to a contact lens made of a hydrophilic gel containing 20 to 95 percent by weight of a swelling agent in the state of equilibrium swelling.
It will be appreciated by those skilled in the art that contact lenses should interfere as little as possible with the normal metabolism of the anterior eye segment, and particularly with the metabolism of the cornea. This minimal interference will extend the time for wearing the lens, without danger of unfavorable consequences for the eye tissues. Many such attempts have been made to serve this purpose.
British Patent No. 1,495,043 is one such attempt. This patent discloses a contact lens made of strongly swollen hydrophilic gels through which oxygen and low-molecular weight water-soluble metabolites diffuse relatively easily. However, very soft contact lenses with a high content of water at the equilibrium swelling at 20.degree. C. (e.g., 60 to 85 percent of water) have low strength and are easily damaged during handling. The refractive index of the lens also decreases rapidly with increasing content by water, so that the lenses with higher dioptric values have to be thicker. In addition, the more water the lens contains, the more the lens dries and absorbs water from the cornea upon application, which may cause a change in refraction, curvature of the cornea, and the like.
What is needed, then, is a contact lens which minimizes interference with the metabolism of the anterior eye segment. This contact lens must also extend the period it can be worn and have improved strength while having high water content. This lens is presently lacking in the prior art.